Monday, December 17, 2012

It has been one year since Comet Lovejoy was watched by SDO, STEREO, and Hinode as it passed by the Sun. Each spacecraft provided unique observations we had not anticipated when they were built and launched. Hinode took an image of the coma in reflected sodium light. SDO and STEREO provided images in the EUV that we continue to analyze. Here is one picture from the movie comet_swoosh_171.mp4 on the SDO Comet Lovejoy Event Page. The streaks across the path of the comet have become the fascinating part of the comet tail.

In the past year we have figured out one way the comet tail can be bright in the solar corona. (Check out the paper at the Physics ArXiv site.) But we still don't know how the solar magnetic field affects (and is affected by) the comet as it moves through. All of that stuff coming off the comet makes the field shake, can we learn something from that? The brightness of the comet debris comes from running into electrons in the corona. Can we learn about the number of electrons in the corona?

We need even bigger sun-grazing comets!

Since Comet Lovejoy we have had only one alert to look for a comet in SDO and we saw nothing. But Comet ISON is due on Thanksgiving Day next year. It was acquired out near Jupiter, which usually means it is a big comet. As it moves toward the Sun, people are watching to see if stays bright. If it does we will be in for quite a show. Comet Lovejoy came in from the south and was seen only in the southern hemisphere. Comet ISON is coming in from the north and could be visible from the United States both inbound and outbound. Comet ISON will also pass through the corona a little farther out than did Comet Lovejoy, 1.2 million km (1.9 million miles) above the Sun's surface.